Lubricant composition and lubricant composition-sealed bearing

ABSTRACT

The present invention provides a lubricant composition which can be used as a lubricant for a rolling component, the composition capable of maintaining enhanced lubrication performance over a long period of time even under high temperature conditions such as temperatures of 180° C. or higher, and a rolling bearing including the lubricant composition sealed therein. A lubricant composition-sealed bearing  1  includes a lubricant composition  7  that is sealed in the peripheries of the rolling bodies  4 . The lubricant composition  7  contains a base oil and an antioxidant. The base oil is an oil mixture of an alkyl diphenyl ether oil and at least one oil selected from a poly-α-olefin oil and an ester oil, and contains the alkyl diphenyl ether oil in an amount of 50% or more by weight of the total base oil. The antioxidant is 2,2,4-trimethyl-1,2-dihydroquinoline or a polymer thereof, and is contained in an amount of 0.1% to 10% by weight of the total lubricant composition.

TECHNICAL FIELD

The present invention relates to a lubricant composition, particularlyto a lubricant composition for lubricating a bearing or other rollingcomponents that maybe used under high temperature conditions (forexample, temperatures of 180° C. or higher). The present invention alsorelates to a rolling bearing including the lubricant composition sealedtherein.

BACKGROUND ART

In the industry, there have been attempts to improve performance of alubricant for rolling components such as a rolling bearing byincorporating various additives into the lubricant. When a rollingbearing or the like is operated under high temperature conditions, alubricant oil or a grease sealed in the bearing may be subjected tooxidative deterioration that is likely to accelerate breakage of alubricating film, and thus the life of lubrication may be shortened.Especially, a lubricating film is more likely to be broken underhigh-temperature and high-speed conditions. The breakage of alubricating film causes metal surfaces of rolling components to becontacted each other, thereby leading to problems such as increasedfrequency of heat generation and frictional wear. Therefore, in order toenhance the high-temperature endurance of lubricant oils or greases forrolling bearings or the like, one or more antioxidants such as an amineantioxidant, a phenolic antioxidant and an organozinc compound have beenused alone or in combination of two or more.

For example, there has been proposed the use of phenolic antioxidantssuch as 2,2′-methylenebis(6-tert-butyl-4-methylphenol), amineantioxidants such as octylated diphenylamine, and sulfur antioxidantssuch as phenothiazine in a lubricant for a bearing (see Patent Document1). Further, in an attempt to provide a grease composition for rollingbearings used in motors with reduced torque and noise, there has beenproposed the use of a low-viscosity ester oil as a base oil, a metalsoap as a thickener, and a combination of liquid hindered amine andtriphenyl phosphorothionate as an antioxidant (see Patent Document 2).

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2005-188557 A

Patent Document 2: JP 2012-162657 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The use of such antioxidants as described in Patent Document 1 or 2,however, may not always provide sufficient performance inhigh-temperature endurance, depending on the type of base oil to be usedin combination with the antioxidant, temperature conditions at the timeof lubrication, and so on. For instance, a phenyl ether synthetic oilwhich is one of base oils of lubricants has good thermal and oxidativestabilities; however, when used under high temperature conditions suchas temperatures of 180° C. or higher, a lubricant containing such an oilmay be incapable of providing sufficient high-temperature endurance,depending on the type of antioxidant employed.

The present invention is directed to overcoming the above-mentionedproblems. It is an object of the present invention to provide alubricant composition which can be used as a lubricant for a rollingcomponent, the composition capable of maintaining enhanced lubricationperformance over a long period of time even under high temperatureconditions such as temperatures of 180° C. or higher, and a rollingbearing including the lubricant composition sealed therein.

Means for Solving the Problem

The present invention provides a lubricant composition used forlubricating a rolling component, containing a base oil and anantioxidant, wherein the base oil is an oil mixture of an alkyl diphenylether oil and at least one oil selected from a poly-α-olefin(hereinafter also referred to as “PAO”) oil and an ester oil, andcontains the alkyl diphenyl ether oil in an amount of 50% or more byweight of the total base oil; and the antioxidant is a compoundrepresented by the following formula (1) or a polymer thereof, and iscontained in an amount of 0.1% to 10% by weight of the total lubricantcomposition:

The base oil may contain the alkyl diphenyl ether oil in an amount of70% to 90% by weight of the total base oil. The base oil may be an oilmixture of the alkyl diphenyl ether oil and the poly-α-olefin oil. Thealkyl diphenyl ether oil may have a kinetic viscosity at 40° C. of 60 to120 mm²/s.

The lubricant composition may be a grease containing a urea compound asa thickener.

The lubricant composition may be used under a high temperature conditionof 180° C. or higher.

The present invention provides a lubricant composition-sealed bearingincluding the lubricant composition of the present invention sealed in aregion to be lubricated.

EFFECT OF THE INVENTION

The lubricant composition of the present invention is obtained byadding, as an antioxidant, a predetermined quinoline antioxidant to abase oil mixture containing a predetermined phenyl ether synthetic oilas a main ingredient. Therefore, the present invention can reduceoxidative deterioration of the lubricant in use under a high temperaturecondition of 180° C. or higher over a long period of time and therebyextend a lubricant life, as compared with other lubricants obtained byadding a different antioxidant to the same base oil. As a result, thepresent invention can increase the service life of a bearing or asimilar rolling component including the lubricant composition sealedtherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a deep groove ball bearing shown as anexample of a lubricant composition-sealed bearing of the presentinvention.

FIG. 2 shows results of high temperature exposure tests.

FIG. 3 shows results of high temperature exposure tests.

FIG. 4 shows results of high temperature exposure tests.

MODE FOR CARRYING OUT THE INVENTION

The lubricant composition of the present invention is used forlubricating a rolling component. In particular, the lubricantcomposition is used in a rolling bearing, a gear, or a component partthereof, and the composition is sealed in a region of the bearing or thelike which is to be lubricated. It is envisaged that the lubricantcomposition is used at a temperature of, for example, 150° C. or higher,particularly 180° C. or higher, up to about 200° C. That is, thetemperature range for the use of the composition is, for example, 150°C. to 200° C., more particularly 180° C. to 200° C.

The present invention includes two embodiments of lubricant compositionas follows: (A) a lubricant oil containing a predetermined base oil anda predetermined quinoline antioxidant as essential components; and (B) agrease containing a predetermined base oil, a thickener, and apredetermined quinoline antioxidant as essential components.

The quinoline antioxidant used in the present invention is a compoundrepresented by formula (1), namely 2,2,4-trimethyl-1,2-dihydroquinoline,or a dimeric or higher order condensate (polymer) thereof. A mixture ofthe compound and polymer may also be used.

The polymer corresponds to “TMDQ”, an anti-oxidizing agent of JIS K6211, with physical properties including: a softening point of 80° C. to110° C., a specific gravity of 1.06 to 1.11 and an ash content of 0.5%or less. Examples of commercially available products that can be used inthe present invention include VANLUBE RD manufactured by VanderbiltChemicals, LLC and NOCRAC (registered trademark) 224 manufactured byOuchi Shinko Chemical Industrial Co., Ltd.

When the above-mentioned lubricant composition is used as a lubricantoil, the quinoline antioxidant is contained in an amount of 0.1% to 10%by weight of the total lubricant composition. A quinoline antioxidantcontent of less than 0.1% by weight may not sufficiently improve thehigh-temperature endurance. A quinoline antioxidant content of more than10% by weight may not only fail to improve the performance of thecomposition, but also cause some problems such as evaporation due todegraded materials of the antioxidant, thus leading to even worseperformance in the high-temperature endurance. The amount of thequinoline antioxidant is preferably 0.3% to 10% by weight, morepreferably 0.3% to 5% by weight, further preferably 0.3% to 2% byweight.

When the above-mentioned lubricant composition is used as a grease, thequinoline antioxidant is contained in an amount of 0.1 to 10 parts byweight based on the total 100 parts by weight of the base oil andthickener. A quinoline antioxidant content of less than 0.1 parts byweight may not sufficiently improve the high-temperature endurance. Aquinoline antioxidant content of more than 10 parts by weight may notonly fail to improve the performance of the composition, but also causesome problems such as evaporation due to degraded materials of theantioxidant, thus leading to even worse performance in thehigh-temperature endurance. The amount of the quinoline antioxidant ispreferably 0.3 parts to 10 parts by weight, more preferably 0.3 parts to5 parts by weight, further preferably 0.3 parts to 2 parts by weight.

The lubricant composition of the present invention contains an oilmixture of (X) an alkyl diphenyl ether oil that is an essentialingredient and (Y) at least one oil selected from a PAO oil and an esteroil, and the oil mixture contains the alkyl diphenyl ether oil in anamount of 50% or more by weight of the total base oil. In the base oilmixture, the weight ratio of (X) to (Y) is preferably X:Y=6:4 to 9:1,more preferably X:Y=7:3 to 9:1, particularly preferably X:Y=7.5:2.5 to8.5:1.5. Especially, when the ratio is X:Y=7:3 to 9:1, that is, when thealkyl diphenyl ether oil is contained in an amount of 70% or more byweight of the total base oil, the quinoline antioxidant is more likelyto be effective in improving the high-temperature endurance.

Examples of the alkyl diphenyl ether oil as an essential ingredientinclude a monoalkyl diphenyl ether oil represented by the followingformula (2), a dialkyl diphenyl ether oil represented by the followingformula (3) and a polyalkyl diphenyl ether.

In the formulae, R₁, R₂ and R₃ each represent an alkyl group having 8 to20 carbon atoms, and are each bonded to a phenyl ring or two phenylrings. Especially, a dialkyl diphenyl ether oil having R₂ and R₃ ispreferable in view of some properties such as heat resistance.

The PAO oil (synthetic hydrocarbon oil) is a mixture of a-olefin orisomerized α-olefin oligomers or polymers. Specific examples ofα-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene,1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene,1-nonadecene, 1-eicosene, 1-docosene and 1-tetradocosene; a mixturethereof is usually used.

Examples of the ester oil include diester oils such as dibutyl sebacate,di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate,ditridecyl adipate, ditridecyl glutarate, and methyl acetyl ricinoleate,aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitateand tetraoctyl pyromellitate, polyol ester oils such as trimethylolpropane caprylate, trimethylol propane pelargonate,pentaerythritol-2-ethylhexanoate and pentaerythritol pelargonate,carbonate ester oils and phosphate ester oils.

In the base oil of the lubricant composition of the present invention,the alkyl diphenyl ether oil preferably has a kinetic viscosity at 40°C. of 50 to 200 mm²/s, more preferably 60 to 120 mm²/s. The total baseoil (oil mixture) preferably has a kinetic viscosity at 40° C. of 30 to200 mm²/s, more preferably 60 to 100 mm²/s in view of low-temperatureproperty and heat resistance.

When the lubricant composition of the present invention is used as agrease, the composition additionally contains a thickener. The thickenerused in the present invention is preferably a urea compound because ofexcellent durability against heat and advantageous performance inintervening into sliding portions of mechanical parts as well as inbeing adhered to the sliding portions.

The urea compound can be prepared by a reaction between a polyisocyanatecomponent and a monoamine component. Examples of the polyisocyanatecomponent include phenylene diisocyanate, tolylene diisocyanate,diphenyl diisocyanate, diphenylmethane diisocyanate, octadecanediisocyanate, decane diisocyanate and hexane diisocyanate. The monoaminecomponent used in the present invention may be an aliphatic monoamine,an alicyclic monoamine or an aromatic monoamine. Examples of thealiphatic monoamines include hexylamine, octylamine, dodecylamine,hexadecylamine, octadecylamine, stearylamine and oleylamine. Examples ofthe alicyclic monoamines include cyclohexylamine. Examples of thearomatic monoamine include aniline and p-toluidine.

The thickener such as a urea compound is incorporated into the base oilto obtain a base grease. The base grease containing a urea compound asthe thickener is prepared by reacting the polyisocyanate component withthe monoamine component in the base oil. The thickener content in thebase grease is preferably 1% to 40% by weight, more preferably 3% to 25%by weight. A thickener content of less than 1% by weight results in apoor thickening effect, thereby making it difficult to prepare asuitable grease. A thickener content of more than 40% by weight makesthe resultant base grease too hard to give a desired effect.

It is preferred that the grease as described above have a workedpenetration (JIS K 2220) within the range of 200 to 350. A workedpenetration of less than 200 may reduce oil separation of the grease,thus leading to poor lubricating performance. On the other hand, agrease with a worked penetration of more than 350 is soft, and isundesirable because of easy flowing out from the area in which thegrease is sealed.

The lubricant composition may contain one or more known additives otherthan the above-mentioned quinoline antioxidant as needed, to the extentthat the purpose of the present invention is not impaired. Examples ofsuch additives include metal inactivators such as benzotriazole,viscosity index improvers such as polymethacrylate and polystyrene,solid lubricants such as molybdenum disulfide and graphite,anticorrosives such as a metal sulfonate and a polyhydric alcohol ester,oil-based agents such as an ester and an alcohol, and other anti-wearagents. These can be added alone or in combination of two or more.

The composition of the present invention that contains the predeterminedquinoline antioxidant with the predetermined base oil can exhibitadvantageously improved high-temperature endurance as compared to acomposition that contains a different antioxidant alone. Whereappropriate, an aromatic amine antioxidant or a phenolic antioxidant maybe used as another antioxidant in combination with the quinolineantioxidant.

The lubricant composition-sealed bearing (rolling bearing) including thelubricant composition of the present invention sealed therein will bedescribed below with reference to FIG. 1. FIG. 1 is a sectional view ofa deep groove ball bearing. In a rolling bearing 1, an inner wheel 2having an inner wheel rolling surface 2 a on the outer periphery surfaceand an outer wheel 3 having an outer wheel rolling surface 3 a on theinner periphery surface are concentrically positioned, and a pluralityof rolling bodies 4 are placed between the inner wheel rolling surface 2a and the outer wheel rolling surface 3 a. These rolling bodies 4 areretained by a cage 5. Further, openings 8 a and 8 b on both the ends inthe axis direction of the inner and outer wheels are sealed by a sealmember 6. A lubricant composition 7, the composition as described above,is sealed at least in the peripheries of the rolling bodies 4. The innerwheel 2, the outer wheel 3 and the rolling bodies 4 are made of bearingsteel which is a ferrous metal. The lubricant composition 7 that is agrease intervenes between the rolling surfaces and the rolling bodies 4to achieve lubrication.

While FIG. 1 presents a ball bearing as an example of the bearing, therolling bearing of the present invention may be other bearings such as acylindrical roller bearing, a conical roller bearing, an automaticaligning roller bearing, a needle roller bearing, a thrust cylindricalroller bearing, a thrust conical roller bearing, a thrust needle rollerbearing, and a thrust automatic aligning roller bearing.

Because the lubricant composition-sealed bearing of the presentinvention includes the above-mentioned lubricant composition sealedtherein, it is possible to reduce oxidative deterioration of thelubricant over a long period of time even under conditions of use at ahigh temperature of 180° C. or higher and a high speed, therebyachieving a long service life of the bearing.

EXAMPLES

The present invention is specifically illustrated, but not limited, bythe following examples and comparative examples.

Example 1 and Comparative Examples 1 to 6

Each lubricant composition in Table 1 was evaluated for high-temperatureendurance by measuring the rate of weight reduction of the compositionwhich was left at a high temperature. As shown in Table 1, each base oilwas an oil mixture of an alkyl diphenyl ether oil and a poly-α-olefinoil at a mixing ratio of 8:2 by weight. Each sample of the lubricantcomposition was left in a constant-temperature bath at 180° C. and at120° C. in an air atmosphere for 0, 200, 400, 600, 800 and 1000 hours(up to 600 hours at 120° C.). The sample was taken out of the bath andweighed at each time point to determine the rate of weight reductionaccording to the following formula. The results are shown in Table 1together with other details. The results of the high temperatureexposure tests at 180° C. and at 120° C. are shown in FIGS. 2 and 3,respectively. In the graphs, the horizontal axis represents time ofmeasurement (h) and the vertical axis represents the rate of weightreduction (wt %).

Rate of weight reduction (wt %)=100×(“weight (g) of lubricantcomposition before being left in constant-temperature bath”−“weight (g)of lubricant composition after being left in constant-temperaturebath”)/“weight (g) of lubricant composition before being left inconstant-temperature bath”

TABLE 1 Example Comparative Example 1 1 2 3 4 5 6 Lubricant compositionBase oil Ether oil¹⁾ + PAO 99 99 99 99 99 99 100 (Ether oil:PAO oil =8:2) Additive Quinoline 1 — — — — — — antioxidant³⁾ Amine — 1 — — — — —antioxidant⁴⁾ Phenolic — — 1 — — — — antioxidant⁵⁾ Sodium sulfite — — —1 — — — Sodium nitrite — — — — 1 — — Arginine — — — — — 1 — Rate ofweight reduction   0 hr. 0 0 0 0 0 0 0  200 hrs. 2.6 2.9 10.8 6.8 8.99.5 4.8  400 hrs. 6.4 6.8 17.2 11.3 13.9 13.5 8.9  600 hrs. 10.1 11.818.9 14.2 15.7 16.5 14.1  800 hrs. 13.0 14.2 22.7 17.3 20.2 19.1 16.31000 hrs. 17.1 18.3 24.9 19.4 22.3 20.8 20.5 Rate of weight reduction  0 hr. 0 0 0 — — — 0  200 hrs. 0.1 0.2 1.2 — — — 0.2  400 hrs. 0.2 0.31.7 — — — 0.7  600 hrs. 0.2 0.4 2.1 — — — 1.1

-   1): MORESCO HILUBE LB100 manufactured by MATSUMURA OIL RESEARCH    CORP., kinetic viscosity at 40° C.: 97 mm²/s-   2): SYNFLUID 801 manufactured by Nippon Steel Chemical Co., Ltd.,    kinetic viscosity at 40° C.: 46 mm²/s-   3): 2,2,4-trimethyl-1,2-dihydroquinoline polymer-   4): octylated diphenylamine-   5): 2,2′-methylenebis(6-tert-butyl-4-methylphenol)

Examples 2 and 3 and Comparative Examples 7 and 8

Each lubricant composition in Table 2 was evaluated for high-temperatureendurance by measuring the rate of weight reduction of the compositionwhich was left at a high temperature. As shown in Table 2, each base oilwas an oil mixture of an alkyl diphenyl ether oil and a poly-α-olefinoil or an ester oil at a mixing ratio (by weight) as indicated in thetable. In Table 2, superscripts 1) to 3) are the same as defined inTable 1. Each sample of the lubricant composition was left in aconstant-temperature bath at 180° C. in an air atmosphere for 0, 200 and400 hours. The sample was taken out of the bath and weighed at each timepoint to determine the rate of weight reduction according to the formuladescribed above. The results are shown in Table 2 together with otherdetails. The results of the high temperature exposure tests are shown inFIG. 4 as those of Example 1, etc.

TABLE 2 Comparative Example Example 2 3 7 8 Lubricant composition (wt %)Base oil Ether oil¹⁾ + PAO oil²⁾ 99 — 100 — (Ether oil:PAO oil = 6:4)Ether oil¹⁾ + Ester — 99 — 100 oil⁶⁾ (Ether oil:Ester oil = 8:2)Additive Quinoline 1 1 — — antioxidant³⁾ Rate of weight reduction [180°C.] (wt %)  0 hr. 0 0 0 0 200 hrs. 8.88 2.85 13.1 3.5 400 hrs. 14.665.39 19.3 6.5 ⁶⁾KAOLUBE 262 manufactured by Kao Corporation, kineticviscosity at 40° C.: 33.5 mm²/s

-   6): KAOLUBE 262 manufactured by Kao Corporation, kinetic viscosity    at 40° C.: 33.5 mm²/s

As shown in Tables 1 and 2 and FIGS. 2 to 4, the compositions ofexamples in which the predetermined quinoline antioxidant was added tothe base oil mixture containing the alkyl diphenyl ether oil as a mainingredient were confirmed to exhibit lower rates of weight reduction inthe high temperature exposure tests as compared to those obtained with adifferent antioxidant added to the same base oil, meaning that oxidativedeterioration can be suppressed over an extended period of time.

INDUSTRIAL APPLICABILITY

The lubricant composition of the present invention can be suitablyapplied for lubrication of rolling components such as a bearing for useunder high temperature conditions (for example, temperatures of 180° C.or higher).

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

-   1 Rolling bearing-   2 Inner wheel-   3 Outer wheel-   4 Rolling body-   5 Cage-   6 Seal member-   7 Lubricant composition-   8 a, 8 b Opening

1. A lubricant composition used for lubricating a rolling component,comprising a base oil and an antioxidant, wherein the base oil is an oilmixture of an alkyl diphenyl ether oil and at least one oil selectedfrom a poly-α-olefin oil and an ester oil, and contains the alkyldiphenyl ether oil in an amount of 50% or more by weight of the totalbase oil; and the antioxidant is a compound represented by the followingformula (1) or a polymer thereof, and is contained in an amount of 0.1%to 10% by weight of the total lubricant composition:


2. The lubricant composition according to claim 1, wherein the base oilcontains the alkyl diphenyl ether oil in an amount of 70% to 90% byweight of the total base oil.
 3. The lubricant composition according toclaim 2, wherein the base oil is an oil mixture of the alkyl diphenylether oil and the poly-α-olefin oil.
 4. The lubricant compositionaccording to claim 1, wherein the alkyl diphenyl ether oil has a kineticviscosity at 40° C. of 60 to 120 mm²/s.
 5. The lubricant compositionaccording to claim 1, wherein the lubricant composition is a greasecontaining a urea compound as a thickener.
 6. The lubricant compositionaccording to claim 1, wherein the lubricant composition is used under ahigh temperature condition of 180° C. or higher.
 7. A lubricantcomposition-sealed bearing comprising the lubricant compositionaccording to claim 1 sealed therein.